Vibration exciter for soil compacting devices

ABSTRACT

A vibration exciter for soil compacting devices, e.g., for a vibration plate, comprises unbalanced shafts. These unbalanced shafts are parallel or coaxial to one another, can be driven in opposite directions with the same rotational speed, and each supports a stationary unbalanced mass and an unbalanced mass that can rotatably move relative to the unbalanced shaft. The relative position of a respective moving unbalanced mass with regard to the unbalanced shaft supporting the same can be adjusted by an adjusting device so that the centrifugal forces produced by the unbalanced masses during the rotation of the unbalanced shafts are entirely canceled out in every position of rotation of the unbalanced shafts. This makes it possible, among other things, to effect a change in the relative position so that the magnitude of a total centrifugal force resulting from the unbalanced masses is proportional to an advancing speed of the soil compacting device.

The present invention relates to a vibration exciter for a soilcompacting device according to the preamble of patent claim 1.

Vibration exciters of this type are used predominantly in vibrationplates, and are known from, for example, EP 0 358 744 B1.

A similar vibration exciter is described in DE 100 38 206 A1. It has twoimbalance shafts that are positively coupled and that are capable ofrotation in opposite directions, each bearing a stationary imbalancemass as well as an imbalance mass that can be moved rotationallyrelative to the stationary imbalance mass, and thus with the imbalanceshaft. The position of the movable imbalance masses can be activelymodified within a large range using adjustment means.

When the imbalance shafts rotate, the cooperation of the differentimbalance masses produces a resulting overall force that can be directedin the forward or backward direction of travel as desired by theoperator. The change of the direction of travel is effected byadjustment means that control the movable imbalance masses. If theoperator wishes to bring the soil compacting device to a standstill, theresulting force of the centrifugal weights is set in the verticaldirection. This also means that a well-directed compacting of the soilcan be achieved while the machine is standing still.

However, the operator does not always desire a strong compacting of thissort at a locally limited point on the soil. In particular when thevibration plate is moving back and forth, at what is called the reversepoint an overly strong and thus disadvantageous compacting of the soilcan arise, because the force acting on the soil at this position is atits greatest, whereas during the forward or backward travel of thevibration plate, and the concomitant pivoting of the resultant forcevector by, for example, 45° towards the front or towards the back, theforce acting on the soil is reduced to 1/%2 of the maximum value.

Although the described arrangements have proven very valuable incompacting soil, sand, or gravel, they can be problematic in thecompacting of asphalt or concrete surfaces, because the maximum verticalforce prevailing at the reverse point can cause localized indentationsthat cannot be corrected. Thus, in asphalt rollers the vibration isstandardly switched off in reverse operation in order to prevent theroller from sinking too deeply into the asphalt when the direction ischanged.

In order to solve this problem, in DE 199 43 391 A1 a vibration exciteris described in which the phase position of the centrifugal weights canbe adjusted in such a way that the vertical components of thecentrifugal forces produced by the centrifugal weights cancel each otherout in each rotational position, while the horizontal components of thecentrifugal forces are correspondingly added together in the samedirection. This makes it possible for the vibration plate to no longercommunicate vertical vibrations to the soil when standing still; rather,via a soil contact plate, shearing stresses are introduced into thesoil, with which cracks and pores, for example in an asphalt surface,can advantageously be compacted.

This arrangement has also proved very effective in practice. However,the strong horizontal vibrations that prevail during the standstilloperation of the vibration plate are not always pleasant for theoperator, and also are not always desired for the compacting of the soilsurface.

The present invention is therefore based on the object of developing avibration exciter of the type named above in such a way that anexcessively strong compacting of the soil in standstill operation, dueto strong vertical vibrations, can be avoided without exposing theoperator or the soil to be compacted to strong countering horizontalvibrations.

According to the present invention, this object is achieved by avibration exciter having the features of patent claim 1. Advantageousdevelopments are defined in the dependent claims.

A vibration exciter according to the present invention preferably hastwo imbalance shafts that stand parallel to one another and that can bedriven in opposite directions with the same rotational speed, eachbearing a stationary imbalance mass and an imbalance mass that can bemoved in rotational fashion relative to the stationary imbalance massand/or to the respective imbalance shaft. Each of the imbalance shaftshas an adjustment means with which the position of each movableimbalance mass can be adjusted in relation to the imbalance shaft thatbears it. According to the present invention, the positions of themovable imbalance masses in relation to the imbalance shafts that bearthem can be adjusted using the adjustment means in such a way that thecentrifugal forces produced by the imbalance masses during the rotationof the imbalance shafts cancel each other out as a whole in eachrotational position of the imbalance shafts. This means that while eachimbalance mass in itself produces a centrifugal force, the centrifugalforces are however adjusted in terms of direction and magnitude in sucha way that they compensate one another in the overall sum. Therefore, inthis operating state (standstill position) the vibration exciterproduces no vibrations, although the imbalance shafts are rotating.

In this way, it can be achieved in particularly advantageous fashionthat the magnitude of the resulting overall centrifugal force, i.e., thevibration strength, can be adjusted dependent on the speed of forwardmotion of the vibration plate. If the speed is reduced, the effectivecentrifugal force is also reduced in a corresponding ratio, down to thepoint at which the machine is standing still, at which point there is nolonger any resultant overall centrifugal force, and thus no longer anyvibration. In this way, a communication of energy into the soil can beachieved that is very uniform over the surface to be compacted.

In a particular specific embodiment of the present invention, therelative position on each of the imbalance shafts can be adjusted suchthat the centrifugal forces of the imbalance masses borne by thisimbalance shaft cancel each other out in each rotational position of theimbalance shaft. This means that even in operation with only oneimbalance shaft a relative position can be achieved in which there is novibration effect.

In order to achieve a forward motion of the soil compacting device as inknown devices, in a preferred specific embodiment of the presentinvention the relative positions can be modified in such a way that thecentrifugal forces of the imbalance masses do not cancel each other out;rather, a resultant overall centrifugal force has a horizontalcomponent. In this way, it is possible to bring about a forward motionof the vibration plate, as is known from the prior art.

When there is a change of direction, for example between a forward and abackward direction of travel, at the transition the already-describedstandstill position can be taken, in which no vibration is communicatedto the soil. In this way, undesirable vertical and/or horizontalvibrations can also be avoided at the reverse point during the change ofdirection. Because the shifting of the movable imbalance masses issufficient to produce the resulting centrifugal force with the desireddirection and magnitude, in a preferred specific embodiment it is notrequired that the phase position of the imbalance shafts to one anotherbe modifiable, as is the case for example in the vibration exciterdescribed in DE 100 38 206 A1.

In the context of this description, the term “imbalance mass” is meantabstractly. An imbalance mass can of course also be made up of aplurality of imbalance elements distributed on the respective imbalanceshaft.

These and additional advantages and features of the present inventionare explained in more detail below with the aid of the accompanyingFigures.

FIG. 1 shows a section, seen from the top, through a vibration exciteraccording to the present invention in the standstill position; and

FIG. 2 shows schematic sections through two imbalance shafts indifferent rotational positions, with the respective positions of theimbalance masses.

As was already mentioned, vibration exciters are known in many differentembodiments. Also known are what are called phase adjustment devices, aspresented for example in DE 199 43 391 A1; these are adjustment devicesfor setting relative positions between imbalance masses and imbalanceshafts. Because the present invention does not relate to the detailedand concrete design of a particular vibration exciter or a particularadjustment device, but rather relates to a relative setting (phaseposition) that is especially suitable for this purpose but has not beenpreviously known, a detailed description of the vibration exciter is notrequired.

Nonetheless, on the basis of FIG. 1 the design of a vibration exciteraccording to the present invention will be briefly described.

In a housing 1, two imbalance shafts 2, 3 are mounted so as to becapable of rotation, imbalance shaft 2 being rotationally driven by adrive (not shown).

Imbalance shaft 2 bears imbalance elements 4 and 5, which are connectedfixedly with imbalance shaft 2 and form a stationary imbalance mass.

In addition, an imbalance mass 6 that is capable of rotational motion issituated on imbalance shaft 2, and this mass can be rotated relative toimbalance shaft 2 via a hub 7 and bearing 8.

The position relative to one another of movable imbalance mass 6 andimbalance shaft 2 is determined with the aid of an adjustment means 9.The principle of action of such an adjustment means has long been known,and is described for example in DE 100 38 206 A1. Adjustment means 9essentially comprises a piston 10 that can be displaced axially underhydraulic action, and that can be moved axially back and forth in ahollow area of imbalance shaft 2. Piston 10 bears a cross-bolt 11 thatpasses through two longitudinal grooves 12 formed in the wall ofimbalance shaft 2 and engages in spiral-shaped grooves 13 that areformed on the inner side of hub 7. When piston 10, and therewithcross-bolt 11, are axially displaced, hub 7 thus rotates relative toimbalance shaft 2, as does movable imbalance mass 6 borne by hub 7.

In addition, imbalance shaft 2 bears a toothed wheel 14 that meshes witha toothed wheel 15 that is attached to imbalance shaft 3. Via toothedwheels 14 and 15, the rotational motion of driven imbalance shaft 2 istransmitted in positive fashion to imbalance shaft 3, which thus rotatesin the opposite direction but with the same rotational speed.

In the same way as imbalance shaft 2, imbalance shaft 3 bears twoimbalance elements 16, 17 that together form a stationary imbalancemass. In addition, an imbalance mass 18 is provided that is capable ofrotational motion on imbalance shaft 3, and its position relative toimbalance shaft 3 can be adjusted using an adjustment means 19. Becauseadjustment means 19 has the same design as adjustment means 9, adetailed description is omitted.

The position of the imbalance mass shown in the sectional view of FIG. 1corresponds to the relative position according to the present invention,in which the individual centrifugal forces produced by the respectiveimbalance masses and/or imbalance elements cancel each other out as awhole (standstill position). This means that the imbalance effect ofimbalance elements 4, 5 and/or 16, 17 on the one hand, and the imbalanceeffect of movable imbalance masses 6, 18 on the other hand, must beidentical in their magnitude but opposed to one another.

The associated mr values (product of mass m×radius r of the center ofthe imbalance mass) must be correspondingly matched to one another.

As a result, imbalance shafts 2 and 3 can accordingly rotate withoutresulting in an outwardly effective imbalance, and thus a vibration.However, when movable imbalance masses 6, 18 are displaced by adjustmentmeans 9, 19, this state of equilibrium is canceled, so that the desiredvertical and horizontal vibrations for soil compacting can arise.

The various relative positions and the vibration states resultingtherefrom are shown in FIG. 2. FIG. 2 shows highly schematized side viewfrom the right in FIG. 1.

The hatched half-circles correspond to movable, i.e. adjustable,imbalance masses 6, 18, while the non-hatched half-circles are intendedto correspond to imbalance masses 4, 5 and 16, 17, which are stationaryrelative to imbalance shafts 2, 3, as can be recognized from field a),“Standstill,” in FIG. 2.

The state shown in FIG. 1 is contained in line a) of FIG. 2 under thecaption “Standstill.” The direction of rotation of imbalance shafts 2,3, and thus of the imbalance masses, is represented by curved arrows.Stationary imbalance masses 4, 5 and/or 16, 17 stand respectivelyopposite movable imbalance masses 6, 18.

In lines a) to d), various rotational states of imbalance shafts 2, 3are shown, each rotated by 90°. The direction of rotation of imbalanceshafts 2, 3 is of course the same each time.

In order to achieve forward motion of the vibration plate (left columnof FIG. 2), movable imbalance masses 6, 18 are rotated in relation tostationary imbalance masses 4, 5 and/or 16, 17.

In the depicted example, movable imbalance mass 6 has been rotated by90° relative to stationary imbalance elements 4, 5, as well as toimbalance shaft 2. Moreover, movable imbalance mass 18 has been rotatedby 90° relative to stationary imbalance elements 16, 17 on imbalanceshaft 3, in the same direction as movable imbalance mass 6. Thecorresponding state is shown in FIG. 2 a), in the column “Forward.” Hereas well, various rotational states of imbalance shafts 2, 3 are shown inthe column “Forward,” under a) to d).

It can be seen that the centrifugal forces resulting from imbalancemasses 4, 5 on the one hand and 6 on the other hand and/or 16, 17 and 18no longer compensate one another, as was the case for standstillvibration. Rather, the centrifugal forces are superposed in such a waythat a resultant force, shown in Figure a), is directed upward and tothe left, corresponding to the forward direction.

In FIG. 2 c) there arises a corresponding counteraction downward and tothe right. In this case, the vibration plate is supported on the soil,and conducts the vibrational energy into the soil.

A backward motion of the vibration plate (to the right in FIG. 2) isshown in the right column of FIG. 2. For this purpose, movable imbalancemasses 6 and 18 have been rotated in relation to imbalance shafts 2, 3that bear them, in the direction opposite the forward direction and by90° relative to the standstill position, as can be seen in FIG. 2 a) inthe column “Backward.”

In this way, a back-and-forth vibration of the vibration plate upwardand to the right or downward and to the left is achieved, resulting inbackward travel, as is shown by straight arrows in Figures a) and c)“Backward.”

The positions of the imbalance masses shown in FIG. 2 are extremepositions. Depending on the construction of adjustment means 9, 19,arbitrary intermediate positions, i.e., displacement angles other than90°, can be achieved, so that a continuous change between forwardtravel, standstill operation, and backward travel can be achieved.

For adjustment means 9, 19, it is possible on the one hand to use knownmeans such as hydraulic controlling, electric motors, electromechanicalcontrol actuators, etc. Alternatively, in a simplified specificembodiment a controlling of the movable imbalance masses can take placewith the aid of simple tension-compression cables that can be controlledby the operator via a common control unit. This can result inconsiderable savings of cost even in simpler vibration plates.

In order to achieve a precise change between the individual operatingstates, the changing of the relative positions using adjustment means 9,19 should be capable of being carried out in synchronous fashion. Ifnecessary, it can however also additionally be useful to enableindividual adjustability of the movable imbalance masses without therequirement of synchronization.

The continuous change between forward and backward travel, in whichstandstill operation can take place without producing vibration, makesit possible to adapt the magnitude of the resulting centrifugal force,and thus the effective vibration, in a manner proportional to the speedof forward motion of the vibration plate. The slower the vibration platetravels, the smaller is the resulting centrifugal force, until, at astandstill point of the vibration plate, e.g. at the reverse point, novibrations are introduced into the soil. This proportional dependencyresults from the design of the vibration exciter according to thepresent invention, without having to make use of expensive controlmeasures.

Of course, with the vibration exciter according to the present inventionit is also possible to assume relative positions other than those shownin FIG. 2. Given a corresponding design of adjustment means 9, 19, forexample, relative positions can be achieved in which in the standstillposition of the vibration plate no vertical vibrations are produced, butstrong horizontal vibrations are produced, as is known from DE 199 43391 A1.

The present invention has been explained in relation to an example of avibration exciter according to FIG. 1. Of course, the underlyingprinciple of the present invention can also be applied to othervibration exciters, for example comprising a plurality of movableimbalance masses or a different number of imbalance shafts.

1. A vibration exciter for soil compacting devices, comprising:imbalance shafts that stand parallel or coaxial to one another and thatcan be driven in opposite directions with the same rotational speed,each of the imbalance shafts bearing an imbalance mass attached to it instationary fashion and an imbalance mass that can be moved in arotational fashion relative to the shaft, and each of the imbalanceshafts having allocated to it an adjustment means for adjusting theposition of the respective movable imbalance mass relative to theimbalance shaft that bears it, wherein during operation, the relativepositions can be adjusted using the adjustment means in such a way thatthe centrifugal forces produced by the imbalance masses during therotation of the imbalance shafts cancel each other out as a whole ineach rotational position of the imbalance shafts, and wherein a changeof the relative positions can be executed in such a way that themagnitude of an overall centrifugal force resulting from the imbalancemasses is proportional to a speed of forward motion of the soilcompacting device.
 2. A vibration exciter according to claim 1, whereinthe relative position on each of the imbalance shafts can be adjusted insuch a way that the centrifugal forces of the imbalance masses borne bythis imbalance shaft cancel each other out in each rotational positionof the imbalance shaft.
 3. A vibration exciter according to claim 1,wherein, in order to effect a forward motion of the soil compactingdevice in a horizontal first direction, the relative positions arecapable of being modified in such a way that the centrifugal forces ofthe imbalance masses do not cancel one another; rather, an overallcentrifugal force resulting from the centrifugal forces has a horizontalcomponent.
 4. A vibration exciter according to claim 3, wherein whenthere is a change between the first direction and an opposite, seconddirection, the relative positions defined in claim 1 are capable ofbeing assumed during the transition.
 5. A vibration exciter according toclaim 1, wherein the change of the relative positions can be executedcontinuously.
 6. A vibration exciter according to claim 1, wherein theimbalance shafts are coupled with one another positively so as to becapable of rotation in opposite directions.
 7. A vibration exciteraccording to claim 1, wherein the phase position of the imbalance shaftsto one another cannot be modified.
 8. A vibration exciter according toclaim 1, wherein the adjustment of the relative positions on theimbalance shafts using the adjustment means can be executedsynchronously.
 9. A vibration exciter according to claim 1, wherein theadjustment means can be actuated electrically, hydraulically,pneumatically, or mechanically.
 10. A vibration exciter according toclaim 1, wherein at least one part of the imbalance masses is formedfrom a plurality of imbalance elements.